Heretofore, a data transmission system and data transmission method of this kind have been disclosed in Patent Publication No. 1647396.
FIG. 1 is a block diagram showing the configuration of a conventional data transmission system. The data transmission system shown in FIG. 1 comprises a transmitting side apparatus 10 and a receiving side apparatus 60.
The transmitting side apparatus 10 comprises a buffer 11, transmit frame creation section 12, modulator 13, transmit radio section 14, antenna 15, antenna duplexer 16, receive radio section 17, demodulator 18, and separator 19.
The receiving side apparatus 60 comprises an antenna 61, antenna duplexer 62, receive radio section 63, demodulator 64, data holding section 65, error detection section 66, transmit frame creation section 67, modulator 68, and transmit radio section 69.
With this kind of configuration, first, in the transmitting side apparatus 10, transmit data is stored in the buffer 11, this stored transmit data is framed by the transmit frame creation section 12, and this transmit frame signal is output to the modulator 13.
After undergoing modulation processing by the modulator 13, the transmit frame signal undergoes predetermined radio processing such as up-conversion by the transmit radio section 14, and after passing via the antenna duplexer 16, is transmitted as a radio signal from the antenna 15.
Then, in the receiving side apparatus 60, a signal received by the antenna 61 is output via the antenna duplexer 62 to the receive radio section 63, where it undergoes predetermined radio processing such as down-conversion, and the resulting signal is output to the demodulator 64.
The received signal is demodulated by the demodulator 64, and this demodulated receive data is held in the data holding section 65 and output to the error detection section 66. The error detection section 66 performs error detection on the receive data. If an error is detected, a signal (hereinafter referred to as “NACK signal”) requesting retransmission is output from the error detection section 66 to the transmit frame creation section 67.
In the transmit frame creation section 67, framing is performed that multiplexes the NACK signal with transmit data, and this transmit frame signal is output to the modulator 68. This transmit frame signal is modulated by the modulator 68, and after undergoing predetermined radio processing by the transmit radio section 69, is transmitted as a radio signal from the antenna 61 via the antenna duplexer 62.
This transmit signal is received by the antenna 15 of the transmitting side apparatus 10, output via the antenna duplexer 16 to the receive radio section 17 where it undergoes predetermined radio processing, and then demodulated by the demodulator 18 and separated into receive data and a NACK signal by the separator 19. The receive data is output to latter-stage receive processing circuitry (not shown), and the NACK signal is output to the buffer 11, whereby the data previously transmitted from the buffer 11 is retransmitted.
This retransmitted data is received in the receiving side apparatus 60 in the same way as described above, and is held combined with the previous receive data in the data holding section 65. This held combined data undergoes error detection by the error detection section 66.
As described above, if an error is detected, a NACK signal is output to the transmit frame creation section 67. If, on the other hand, no error is detected, a transmission request signal (hereinafter referred to as “ACK signal”) requesting transmission of the next data from the transmitting side apparatus 10 is output to the transmit frame creation section 67.
The above-described series of operations is repeated until an ACK signal is obtained in this way. When an ACK signal is obtained, the data in the data holding section 65 is considered to be receive data, and is output to latter-stage receive processing circuitry (not shown). Following this output, that receive data is eliminated from the data holding section 65.
When an ACK signal is input to the transmit frame creation section 67, the transmit frame creation section 67 performs framing that multiplexes the ACK signal with transmit data. This transmit frame signal is transmitted to the transmitting side apparatus 10 as described above.
In the transmitting side apparatus 10, the received ACK signal is output to the buffer 11, and the data for which that ACK signal was obtained is eliminated from the buffer 11. Then, transmission of the next data begins.
As described above, in a conventional data transmission system, receive data error detection is carried out by the receiving side apparatus, and if an error is detected a retransmission request is made to the transmitting side apparatus. In response to this, an operation to retransmit the same data is repeated, so that eventually there is no data error in the receiving side apparatus.
However, with conventional apparatuses, in response to a retransmission request from the receiving side, an operation that performs retransmission on the transmitting side is simply repeated until there is no data error on the receiving side, and there is thus a problem in that, if the retransmitted data is not appropriate, the number of retransmissions will be large and transmission efficiency will degrade.